Wards. We all buy them, or at least we should. We place them at the keyspots of a map to gain vision and that enables possible ganks and buff steals. Yet wards have another use (apart from eating your gold)! They have the ability to interrupt projectiles!
So how does it work? It's pretty simple: You are playing and suddenly a Rammus charges at you from the bushes with his Powerball. You won't survive if he Taunts you and you won't be able to get away if he bumps into you. So what do you do? You place a Ward in front of Rammus and he bumps into the Ward while you can happily flee.
As demonstrated in the video below:
Skip to 9:00 and watch how Rammus gets eaten
This works for all sorts of abilities; like Morgana's Dark Binding, Blitzcrank Rocket Grab, Amumu's Bandage Toss and any other skill shot. Some skillshots are not worth to be blocked by Wards because they are too spammable. Abilities like Mundo's Cleaver and Corki's Missile Barrage. You want to block a stun/snare/grab at the most crucial moments.
This can also be executed with other things, namely Teemo's Noxious Traps, Shaco's Jax in the Box and any other pet.